Short answers, pulled from the story.
Seoul's history traces back to 18 BC, when it was founded by the people of Baekje, one of the Three Kingdoms of Korea. Baekje's capital was at Wiryeseong, believed to have stood within the bounds of the ramparts Pungnaptoseong and Mongchontoseong in what is now southeastern Seoul.
Seoul is the only special metropolitan city in South Korea. The status grew from the Charter of the City of Seoul, published by the U.S. military government on the 10th of October 1946, which established Seoul as an independent administrative unit separate from any province.
Seoul changed hands four times during the Korean War. It fell to North Korean forces in June 1950, was retaken by UN forces in September 1950, fell again to a combined Chinese and North Korean force in January 1951, and was recaptured by UN forces during Operation Ripper in the spring of 1951.
The Constitutional Court of Korea ruled in 2004 that Seoul must remain the national capital because that status is an unwritten constitutional custom. It can be changed only by a nationwide referendum, even though the planned city of Sejong has taken on many administrative functions.
Seoul is a native Korean common noun meaning capital city, believed to have descended from Seorabeol, which originally referred to Gyeongju, the capital of Silla. French missionaries wrote the colloquial name as Seoul, which is why that romanization persists across languages today.
Seoul hosted the 1986 Asian Games, the 1988 Summer Olympics and Paralympic Games, and the 2010 G20 Seoul summit. It also served as one of the host cities of the 2002 FIFA World Cup, with the Seoul World Cup Stadium staging the opening ceremony and first game.